1. Field of the Invention
The present invention relates to an optical medium judging method, and particularly, to a method for avoiding the collision of an objective lens with a disk or the failure to judge a warped disk.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a perspective diagram showing a pickup head and the relating devices reading a disk 20 in a prior art optical disk drive. The pickup head comprises a laser diode 10 for emitting a laser beam with a predetermined wavelength. After this beam passes through a polarization beam splitter (PBS) 11, a collimating lens 12 will converge it to be a parallel beam. This parallel beam will pass through a quarterwave plate 13, and the quarterwave plate 13 will make the linearly polarized beam to become a circularly polarized beam. The circularly polarized beam will pass through an objective lens 14, and the objective lens 14 will focus it so as to form a focusing spot SP on the disk. A driving circuit 30 will drive an actuator 32 for controlling the objective lens 14 to move forward and backward along the direction of the protracting light axis and to change the position of the focusing spot SP. Therefore, the focusing spot SP will be focused on the data layer of the disk. After the reflective light of the data layer of the disk makes the focusing spot SP reversely pass through the objective lens 14, the quarterwave plate 13, the original circular polarization will become the linear polarization, and then the pass through the collimating lens 12 so as to achieve the polarization beam splitter 11. At this time, the reflective beam is reflected to a focusing lens 15 and then received by a light detector 16 because the direction of the linear polarization is perpendicular to the original direction of the polarization.
FIG. 2 is a perspective diagram of reflection amount when normally judging the disk in the prior art. The horizontal axis represents the time, while the vertical axis represents the reflection signal. At t1, a reflection signal amount peak P1 is detected, and at t2, a reflection signal amount peak P2 is detected.
FIG. 3 is a perspective diagram of an output voltage of a driving circuit 30 when normally judging the disk in the prior art. The horizontal axis represents the time, while the vertical axis represents the output voltage of the driving circuit 30. At t0, the output voltage is V0, and at t1, the output voltage is V1, and at t2, the output voltage is V2, and at t3, the output voltage is V3. The unit of the time axis is corresponding to FIG. 2, the perspective diagram of the reflection amount when normally judging the disk in the prior art.
Please refer to FIG. 3. At t0, the driving circuit 30 will output the voltage V0 so as to make the objective lens 14 shown in FIG. 4A under the home position H0. At this time, the focusing spot SP is not focused on the disk 20, and therefore, in FIG. 2, the perspective diagram of the reflection amount when normally judging the disk in the prior art, at t0, the detected reflection signal amount is not greater than the predetermined value S1. Thus, the reflection signal is not obtained.
Please refer to FIG. 3 again. From t0 to t1, the output voltage of the driving circuit 30 is increased from V0 to V1 so as to make the actuator 32 in FIG. 4A move the objective lens 14 from the position of the home position H0 to the position of the objective lens 14 in FIG. 4B. At this time, the focusing spot SP is in touch with the plastic layer PL1 of the disk 20. Therefore, in FIG. 2, the perspective diagram of the reflection amount when normally judging the disk in the prior art, at t1, the detected reflection signal amount is greater than the predetermined value S1, and a first reflection peak P1 is obtained.
Please refer to FIG. 3 again. From t1 to t2, the output voltage of the driving circuit 30 is increased from V1 to V2 so as to make the actuator 32 in FIG. 4B move the objective lens 14 to the position of the objective lens 14 in FIG. 4C. At this time, the focusing spot SP is in touch with the reflection layer RF1 of the disk 20. Therefore, in FIG. 2, the perspective diagram of the reflection amount when normally judging the disk in the prior art, at t2, the detected reflection signal amount is greater than the predetermined value S1. Thus, a second reflection peak P2 is obtained.
Please refer to FIG. 3 again. From t2 to t3, the output voltage of the driving circuit 30 is increased from V2 to V3 so as the make the actuator 32 in FIG. 4C move the objective lens 14 to the position of the objective lens 14 in FIG. 4D. At this time, the focusing spot SP is not focused on the disk 20, and therefore, in FIG. 2, the perspective diagram of the reflection amount when normally judging the disk in the prior art, at t3,the detected reflection signal amount is not greater than the predetermined value S1, Thus, the reflection signal is not obtained.
Furthermore, FIG. 3 shows the perspective diagram of the output voltage of the driving circuit when normally judging the disk. The operation of judging the disk is initiated at t0, and at this time, the fixed voltage outputted by the driving circuit 30 is increased from V0 to V3 so as to make the actuator 32 in FIG. 4A move the objective lens 14 from the home position H0 to the mechanical maximum H2 in FIG. 4D so that the focusing spot SP will sequentially pass through the plastic layer (PL1) and the reflection layer (RP1) of the disk 20. The distance difference of the beams Y separately reflected by the plastic layer (PL1) and the reflection layer (RF1) is measured so as to judge the type of the disk 20.
To be more detailed, FIG. 5 is a perspective diagram of the measure result of the reflection signal of a prior art disk judging method. The horizontal axis represents the time, and the vertical axis separately shows the detected reflection amounts of the different types of disks (DVD, CD). As for the focusing spot, the plastic layer will generate micro reflection peak P1, and the reflection layer will generate a greater reflection peak P2. As for the DVD disk, the distance of the two peaks is 0.6 mm, and the difference of the generation times of the two peaks is tA t0. As for the CD disk, the distance of the two peaks is about 1.2 mm, and the difference of the generation times of the two peaks is tB t0. By judging the interval of the generation times of the two peaks is tA t0, the distance of the two peaks or the difference of generation times, the type of the disk is determined.
Please refer to FIG. 3 again. The fixed voltage outputted by the driving circuit 30 is increased from V0 to V3 so as to make the actuator 32 in FIG. 4 move the objective lens 14 from the home position H0 to the mechanical maximum H2 shown in FIG. 4D. However, when the disk 20 is warped, the position of the disk 20 will be higher or lower than the normal position because of the warping. When the position of the plastic layer (PL1) of the disk 20 is lower than H2 for the warping, the objective lens 14 will collide with the disk 20. When the position of the plastic layer (PL1) of the disk is exceedingly high for the warping, the focusing spot SP of the objective lens 14 cannot pass through the plastic layer (PL1) or the reflection layer (RF1) of the disk 20. Thus, the operation of judging the disk cannot be performed.
FIG. 6 is a perspective diagram of the reflection amount when the position of the disk is exceedingly low during the operation of judging the disk in the prior art. The horizontal axis represents the time, and the vertical axis represents the reflection signal. At t1, a reflection signal amount peak P1 is detected, and at t2, a reflection signal amount peak P2 is detected.
FIG. 7 is a perspective diagram of the output voltage of the driving circuit when the position of the disk is exceedingly low during the operation of judging the disk in the prior art. The horizontal axis represents the time, and the vertical axis represents the output voltage of the driving circuit 30. At t0, the output voltage is V0, and at t1, the output voltage is V1, and at t2, the output voltage is V2, and at t3,the output voltage is V3. The unit of the time axis is corresponding to FIG. 6, the perspective diagram of the reflection amount when the position of the disk is exceedingly low during the operation of judging the disk in the prior art.
Please refer to FIG. 7. At t0, the driving circuit 30 outputs the voltage V0 to make the objective lens 14 in FIG. 8A positioned at the home position H0. At this time, the focusing spot SP is not focused on the disk 20. In FIG. 6, the perspective diagram of the reflection amount when the position of the disk is exceedingly low during the operation of judging the disk in the prior art, the detected reflection signal amount is not greater than the predetermined value S1 at t0. Therefore, the reflection signal is not obtained.
Please refer to FIG. 7. From t0 to t1, the output voltage of the driving circuit 30 is increased from V0 to V1 so as to make the actuator 32 in FIG. 8A move the objective lens 14 from the position of the home position H0 to the position of the objective lens 14 in FIG. 8B. At this time, the focusing spot SP is in touch with the plastic layer PL1 of the disk 20. Therefore, in FIG. 6, the perspective diagram of the reflection amount when the position of the disk is exceedingly low during the operation of judging the disk in the prior art, the detected reflection signal amount is greater than the predetermined value S1 at t1, and the first reflection peak P1 is obtained.
Please refer to FIG. 7 again. From t1 to t2, the output voltage of the driving circuit 30 is increased from V1 to V2 so as to make the actuator 32 in FIG. 8B move the objective lens 14 to the position of the objective lens 14 in FIG. 8C. At this time, the focusing spot SP is in touch with the reflection layer RF1 of the disk 20. Therefore, in FIG. 6, the perspective diagram of the reflection amount when the position of the disk is exceedingly low during the operation of judging the disk in the prior art, the detected reflection signal amount at t2 is greater than the predetermined value S1, and the second reflection peak P2 is obtained.
Please refer to FIG. 7. From t2 to t3,the output voltage of the driving circuit 30 is increased from V2 to V3 so as to make the actuator 32 in FIG. 8C move the objective lens 14 to the position of mechanical maximum H2 shown in FIG. 8D. At this time, because the position of the disk 20 is exceedingly low, the objective lens 14 will collide with the disk 20 when it moves to H2, and the focusing spot SP is not focused on the disk 20. Therefore, in FIG. 6, the perspective diagram of the reflection amount when the position of the disk is exceedingly low during the operation of judging the disk in the prior art, the detected reflection signal amount at t3 is not greater than the predetermined value S1. Thus, the reflection signal is not obtained.
FIG. 9 is a perspective diagram of the reflection amount when the position of the disk is exceedingly high during the operation of judging the disk in the prior art. The horizontal axis represents the time, and the vertical axis represents the reflection signal. At t2, a reflection signal amount peak P1 is detected.
FIG. 10 is a perspective diagram of the output voltage of the driving circuit when the position of the disk is exceedingly high during the operation of judging the disk in the prior art. The horizontal axis represents the time, and the vertical axis represents the output voltage of the driving circuit 30. At t0, the output voltage is V0, and at t1, the output voltage is V1, and at t2, the output voltage is V2. The unit of the time axis is corresponding to FIG. 9, the perspective diagram of the reflection amount when the position of the disk is exceedingly high during the operation of judging the disk in the prior art.
Please refer to FIG. 10. At t0, the driving circuit 30 outputs the voltage V0 so as to make the objective lens 14 shown in FIG. 11A positioned at the home position H0. At this time, the focusing spot SP is not focused on the disk 20. Therefore, in FIG. 9, the perspective diagram of the reflection amount when the position of the disk is exceedingly high during the operation of judging the disk in the prior art, the detected reflection signal amount at t0 is not greater than the predetermined value S1. Thus, the reflection signal is not obtained.
Please refer to FIG. 10 again. From t0 to t1, the output voltage of the driving circuit 30 is increased from V0 to V1 so as to make the actuator 32 shown in FIG. 11A move the objective lens 14 from the position of the home position H0 to the position of the objective lens 14 shown in FIG. 11B, and finally to the position of the objective lens 14 shown in FIG. 11C. At this time, the focusing spot SP is not in touch with the plastic layer PL1 of the disk 20. Therefore, in FIG. 9, the perspective diagram of the reflection amount when the position of the disk is exceedingly high during the operation of judging the disk in the prior art, the reflection signal amount detected at t1 is also smaller than the predetermined value S1. Thus, the reflection signal is not obtained.
Please refer to FIG. 10 again. From t1 to t2, the output voltage of the driving circuit 30 is increased from V1 to V2 so as to make the actuator 32 in FIG. 11C move the objective lens 14 to the position of the mechanical maximum H2 shown in FIG. 11D. At this time, the focusing spot SP is in touch with the plastic layer PL1 of the disk 20. Therefore, in FIG. 9, the perspective diagram of the reflection amount when the position of the disk is exceedingly high during the operation of judging the disk in the prior art, the reflection signal amount detected at t2 is greater than the predetermined value S1. Thus, a reflection peak P1 is obtained.
Please refer to FIG. 11D. Because the position of the disk 20 is exceedingly high, the focusing spot SP on the measure beam Y only can be in touch with the plastic layer PL1 of the disk 20, but cannot pass through the reflection layer RF 1 when the objective lens 14 moves to the mechanical maximum H2. Therefore, in FIG. 9, the perspective diagram of the reflection amount when the position of the disk is exceedingly high during the operation of judging the disk in the prior art, only a reflection peak P1 is generated. This causes the type of the disk 20 cannot be judged.